1. Field
The subject matter disclosed herein relates to determining a spatial alignment of an inertial measurement unit (IMU).
2. Information
Navigational aids have long been important for commerce and travel. For hundreds or thousands of years, travelers had to rely on paper maps or the verbal directions of a friendly stranger to find their way to a given destination. In contrast, electronic navigational aids have been developed over the last few decades. Because of their original size, expense, and complexity, they were initially used primarily by the military, other governmental entities, and large common carriers, such as ocean liners and airplanes. Recently, however, some electronic navigational aids have become smaller, cheaper, and simpler to use. They have therefore become available to a wider array of people.
In comparison to traditional navigational aids, electronic navigational aids may more easily keep their navigational information current, may offer a greater wealth of navigational information, may offer additional features that were previously not possible, and so forth. For example, modern navigational aids may be capable of offering any of many navigational-related features that may include, but are not limited to: providing general directions, plotting courses between origins and destinations, displaying maps, presenting so-called turn-by-turn directions, recording a path that has been traveled, combinations thereof, and so forth.
An example type of electronic navigational aid uses a satellite positioning system (SPS) in conjunction with an inertial navigation system (INS). This type of electronic navigational aid, which is at times referred to as an SPS-INS navigational system, uses an IMU. To operate such an SPS-INS navigational system, the spatial alignment of the IMU is determined to some level of precision with respect to an earth centered earth fixed (ECEF) coordinate frame.
As indicated above, some navigational aids are implemented in relatively small packages, including some devices that are capable of being carried by an individual. Such portable devices can also be made sufficiently inexpensive so as to be considered affordable by many people. Unfortunately, the size and cost reductions that have been implemented for devices having navigational-aid-related features can produce negative results. More specifically, such devices may be generally less capable of determining a sufficiently accurate spatial alignment of an IMU. Consequently, in certain situations it can be difficult, onerous, or even impossible to use such devices with an SPS-INS navigational system.